In the field of this kind of image display device, various types of image display devices with different aspect ratios are here to stay, such as an image display device capable of displaying an image in aspect ratio of 4:3 and an image display device capable of displaying an image in aspect ratio of 16:9.
For example, there are two types of image display devices: an image display device (also referred to as a first image display device) having a display section DP10 (FIG. 22B) capable of displaying an image in aspect ratio of 3:2 (720×480 pixels); and an image display device (also referred to as a second display device) having a display section DP20 (FIG. 22B) capable of displaying an image in aspect ratio of 8:6 (640×480 pixels).
On the other hand, as shown in FIG. 22A, there is image data D10 which was produced in order for the first image display device with aspect ratio of 3:2 to display an image P10. When the image data D10 is supplied to the first image display device, the first image display device displays, based on the image data D10 supplied, a screen SC10 on the display section DP10 as shown in FIG. 22B. In this case, the image 10 on the screen SC10 is displayed in a horizontal-to-vertical ratio of 1:1 (horizontal and vertical size: 72×72) which is intended by a creator who creates the image P10.
However, if the image data D10 is supplied to the second image display device, the second image display device displays, based on the image data D10 supplied, the whole screen SC10 within the display section DP20 with aspect ratio of 8:6. This changes the shape of the image DP10 on the screen SC10, displaying the image P10 in a different horizontal to vertical ratio (≠1:1, i.e. in the horizontal and vertical size of 64×72) not intended by the creator. This may cause a problem regarding copyright.
The following is one way to solve the problem. In this case, to adjust a horizontal-to-vertical ratio of an image, an image display device previously performs a process to compress or enlarge image data in vertical or horizontal direction (this process will be referred to as a horizontal-to-vertical ratio adjustment process). This keeps a horizontal-to-vertical ratio of the image displayed on a display section in line with creator's intention (For example, Patent Document 1).    Patent Document 1: Japanese Patent Publication No. 2000-227785